I added two background fills to a region, both using color paint, only the second with an inset. the final result is wrong, the second fill looks like a gradient (see picture)

Here is the code:
public class HelloRegion extends Application {
    public static void main(String[] args) {
// System.setProperty("prism.order", "sw");
// System.setProperty("prism.order", "j2d");
        Application.launch(args);
    }
    
    @Override
    public void start(Stage stage) throws Exception {
        Region region = new Region();
        
        region.setLayoutX(10);
        region.setLayoutY(10);
        region.setPrefWidth(100);
        region.setPrefHeight(100);
        
        BackgroundFill b1 = new BackgroundFill(Color.RED, null, null);
        BackgroundFill b2 = new BackgroundFill(Color.BLUE, new CornerRadii(30), null);
        BackgroundFill b3 = new BackgroundFill(Color.YELLOW, null, new Insets(40));
// region.setBackground(new Background(b1, b2, b3));
      region.setBackground(new Background(b1, b3));
        
        Group group = new Group();
        group.getChildren().add(region);
        Scene scene = new Scene(group, 300, 300/*, Color.VIOLET*/);
        stage.setTitle(getClass().getCanonicalName());
        
        stage.setScene(scene);
        stage.show();
    }

}